The present invention relates to an apparatus for controlling venting of fuel vapor from a vehicle fuel tank. More particularly, the present invention relates to a venting apparatus adapted to use pressurized fuel vapor from the fuel tank to initiate fuel vapor venting to a fuel vapor treatment device.
Vehicle fuel tanks are typically equipped with devices for venting fuel vapor from the fuel tank to a remote vapor treatment device. Well-designed venting devices rapidly vent large volumes of fuel vapor from the fuel tank in response to fuel vapor pressure buildup in the tank. Such devices also minimize fuel vapor venting during conditions in which venting would be undesirable, such as during vehicle refueling or during an emergency such as vehicle rollover. Venting devices are also preferably designed to open during development of sub-atmospheric pressure in the fuel tank to allow ambient air to flow into the fuel tank to return tank pressure to acceptable levels.
Designers have proposed various head valve arrangements in an attempt to provide a fuel vapor control valve that opens and closes quickly in response to changes in fuel vapor pressure conditions in the fuel tank. It is known to position a head valve so that pressurized fuel vapor in the fuel tank reaches the head valve and moves the head valve away from a "closed" vent-blocking position to an "opened" position to allow venting of pressurized fuel tank vapor. As the fuel vapor continues to vent, the pressure decreases and the head valve returns to its closed, vent-blocking position. For example, in U.S. Pat. No. 4,760,858 to Szlaga, a ball is used as a head valve.
Designers have also attempted to provide vacuum-assisted fuel vapor-venting assemblies. These assemblies depend upon an external source of vacuum to lift the valve off its valve seat rather than relying upon the pressure head developed by the fuel vapor in the fuel tank. For example, in U.S. Pat. No. 5,156,178 to Harris, an engine-controlled diaphragm valve is used in which the upper side of the diaphragm valve is exposed to vacuum from a vacuum source when the engine is running.
It would be desirable to provide a venting assembly including an improved head valve which moves rapidly to vent relatively large amounts of fuel vapor whenever the fuel vapor pressure in the fuel tank reaches a set level. It would further be desirable to provide a venting assembly including an improved head valve with a vacuum assist.
According to the present invention, an apparatus is provided for controlling venting of fuel vapor from a vehicle fuel tank. The apparatus includes a housing, a valve movable in the housing, a partitioning member, and a spring normally biasing the valve into engagement with the partitioning member. The housing is formed to include an inlet for receiving fuel vapor from the vehicle fuel tank and an outlet for discharging fuel vapor to a vapor treatment device. The valve cooperates with the housing to define a first vent chamber receiving fuel vapor from the fuel tank by way of the inlet and a second vent chamber discharging fuel vapor to the outlet and exposed to pressure from the vapor treatment device.
Thus, the pressure in the first vent chamber is generally equal to the fuel vapor pressure in the fuel tank, while the pressure in the second vent chamber is generally equal to the pressure at the vapor treatment device, which is atmospheric when the vehicle engine is off and slightly sub-atmospheric when the vehicle engine is on. The valve includes a central portion, an outer annular portion, and a first vent opening formed in the central portion to communicate fuel vapor from the first vent chamber and the second vent chamber.
The partitioning member is positioned in the first vent chamber for engagement with the valve. When the valve engages the partitioning member, flow of fuel vapor from the first vent chamber to the second vent chamber through the opening is blocked. The partitioning member partitions the first vent chamber into a central region exposed to pressure from the second vent chamber and an outer annular region exposed to fuel vapor pressure from the inlet. The partitioning member is formed to include an opening providing a flow path between the inlet and the outer annular region.
Thus, advantageously, the valve may be said to be "atmospherically balanced" in that the central portion of the valve is exposed on one side to the pressure in the second vent chamber, which is normally atmospheric or sub-atmospheric, and on the other side to pressure in the central region, which is also atmospheric because the central region always remains in fluid communication with the second vent chamber. The outer annular portion of the valve is exposed on one side to pressure in the outer annular region (usually tank pressure) and on the other side to pressure in the second vent chamber (atmospheric or slightly sub-atmospheric). By thereby "balancing" the valve across its central portion and allowing pressure imbalance across the outer annular portion of the valve, the valve's opening point (the point at which it disengages from the insert in response to buildup of fuel vapor pressure in the outer annular chamber) can be more readily controlled so that high volumes of fuel vapor can be vented from the first vent chamber to the second vent chamber and subsequently to the vapor treatment device at relatively high rates.
In another aspect of the present invention, the partitioning member is formed to include a relief valve chamber, and the apparatus further comprises a vacuum-relief valve movable in the relief valve chamber between a closed position blocking flow between the relief valve chamber and the central region and an open position allowing flow between the relief valve chamber and the central region. Advantageously, when the fuel vapor pressure in the fuel tank drops to below a predetermined level, the vacuum-relief valve moves to the open position to allow ambient air to flow from the second vent chamber to the central region and to the relief valve chamber, passing from there through the inlet to the fuel tank.
In accordance with yet a further aspect of the invention, a first and a second spring plate are disposed on either end of the spring and the apparatus further comprises means for moving the first spring plate relative to the second spring plate. Thus, advantageously, the tension on the spring can be adjusted to precisely establish the opening point of the valve.
In other aspects of the present invention, the atmospherically-balanced vent valve comprises a diaphragm head valve having a vent opening formed in its central portion. One side of the diaphragm head valve is normally exposed to pressure communicated from the fuel vapor treatment device. This pressure is substantially atmospheric when the engine is off, but may be slightly sub-atmospheric when the engine is running because a light vacuum is applied through the fuel vapor treatment device.
The other side of the diaphragm head valve is exposed to fuel vapor pressure from the fuel tank across its outer portion and pressure from the fuel vapor treatment device across its central portion. That is, both sides of the diaphragm are exposed to pressure from the fuel vapor treatment device across the central portion, thus "atmospherically balancing" the diaphragm head valve.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.